While the concepts involved in the system and apparatus herein disclosed and claimed are believed to have application beyond the specific field for which they were developed, the invention was made in connection with the machining of the so-called composite materials which are used in substitution for metal as the surfaces and structural components of aircraft.
The composite materials now in use may be fibers in strand form or as woven textiles which are impregnated with or embedded in a matrix of a heat curable thermosetting resin. When constructing sheets or shells, these materials are laid incrementally upon a work surface having the desired final contour of the intended aircraft component, with the embedded fibers oriented in the directions of the principal strength requirements, and with a sufficient number of layers of the impregnated fibrous building elements, usually tapes or webs, to provide the necessary cross-sectional thickness to the component, or even to localized areas thereof.
When the component is laid up, layer upon layer, and subsequently cured, the matrix of this composite structural material is rigidified, and, because it is destined for precision assembly either with other like parts, or with internal framing structure, it must be trimmed precisely to size and also to facilitate assembly.
The cutting methods evolved for the machining of these materials, because of the nature of the material, have departed somewhat from typical metal machining technology employing milling tools having distinct or readily discernible cutting edges, and are built upon high-speed abrasion in which the cutting edges, although discrete, are barely discernible because the cutting particles are small and positioned randomly on the surface of the cutter. A favored material is diamond crystal embedded in a metal coating formed upon the surface of a rotary steel tool.
Analogizing to milling methods and to milling cutters for the sake of this disclosure, the tools employed for edge trimming may be thought of as comparable to end mills, while for dressing or planing sizeable sections of surface, for example, reducing edge thicknesses for joining the composite shells to internal aircraft structure, the analogous milling technique is face milling.
As between the two techniques, face milling by its nature produces large volumes of dust in the form of minute particles of the composite material, fibers and matrix, which must be collected and removed from the machining site and disposed of. The particles vary on average from 0.0002 to 0.003 inches in size when using cutters having abrasive particles of 30 mesh. The particles are relatively light in weight and, when airborne, settle relatively slowly and indiscriminately, creating manufacturing processing problems because the fibrous material rendered particulate in the machining process is typically graphite, whose airborne invasion of adjacent electrical controls can cause a myriad of unintended electrical results, and because the dust can accumulate detrimentally on the way surfaces of the machine, and contaminate the lubrication systems.
It is accordingly the object of this invention to provide an efficient apparatus and system for the expeditious removal of the particulate composite material from the cutting site where it is generated, and transporting it to remote storage for periodic disposal.